Model salamanders, in a cave

Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at darrennaish.wordpress.com. He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at tetzoo.com! Follow on Twitter @TetZoo.

Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at darrennaish.wordpress.com. He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at tetzoo.com! Follow on Twitter @TetZoo.

While on a family holiday recently I visited Dan yr Ogof, the famous National Show Cave for Wales. Besides being interesting for the expected geological and speleological reasons, Dan yr Ogof is set within landscaped gardens that, bizarrely, feature one of Europe’s largest ‘dinosaur parks’. Great plastic models of tyrannosaurs, sauropods and all manner of other prehistoric creatures litter the surrounds – it seems people somehow associate geological attractions with life-size models of extinct animals. Anyway, I’m not here to talk about those, but instead about some other, less spectacular animal models on display at Dan yr Ogof. Namely, the model salamanders that ‘live’ in small, shallow pools within one of the several caves.

I actually visited Dan yr Ogof as a child, many years ago, and remember the salamanders from then. These models [see adjacent image] of long, pink, aquatic animals depict White olms Proteus anguinus anguinus, the famous cave-dwelling proteid salamanders of the Dinaric karst region in south-eastern Europe. The models are about right in proportions and digit number (olms only have three fingers and two toes), but lack the bushy external gills of the real thing. White olms are committed to cave life, though the recently discovered Black or Brown olm P. a. parkelj is not as specialised and inhabits surface waters. I’ve written about olms a few times on Tet Zoo before, see the links below for more.

Two model Fire salamanders at Dan yr Ogof together; I think there are three in total. Photo by Darren Naish.

There are also some model Fire or Spotted salamanders Salamandra salamandra. Like olms, Fire salamanders don’t occur in Wales or elsewhere in the UK, and – in contrast to continental Europe – there isn’t any indication (so far as I know) that they occurred here in the geological past either (Böhme 2010). Fire salamanders are spectacular, robust, predominantly terrestrial salamandrid salamanders that can reach 30 cm in total length. A substantial amount of geographical variation in size and pigmentation has led to the naming of numerous subspecies and other variants (see Köhler & Steinfartz 2006), and some populations once included within S. salamandra are now classified as distinct species (see Steinfartz et al. 2000).

Fire salamanders aren’t, ordinarily, cave-dwellers, but they might sometimes be found within them: amphibians of many kinds often wander into caves, either to take refuge from conditions outside (it being variously too dry, too hot, or too cold), or because they get washed in by floodwaters or such. There are many tales of people finding, or knowing of, frogs and toads that have obviously been living in a given cave for years or even decades (cavers often talk of ‘rescuing’ frogs and toads found deep inside caves and returning them to the surface. I appreciate the sentiment, but are you sure you’re ‘rescuing’ the animal? It might have been there deliberately). It doesn’t take much imagination to see how such animals might, over generations, give rise to cave-dwelling specialists that lack pigmentation, have atrophied eyes, and are behaviourally and ecologically specialised for cave life. Maybe amphibians are pre-adapted for this so-called stygobiontic or troglodytic lifestyle since many find mates using olfactory or chemosensory cues, have long lifespans and low metabolisms, and are well suited for perpetual existence in wet, cool, dark conditions.

Female Guajon; image by Jan P. Zegarra, U.S. Fish and Wildlife Service, and in public domain.

Why have anurans (frogs and toads) never produced a dedicated stygobiontic form (so far as we know)? Firstly, their reliance on acoustic cues to find mates might make it difficult for them to survive for generations in places where roaring water is often a common feature*. Secondly, their (typically) herbivorous tadpoles might also not be able to survive in the majority of caves. Then again, roaring water is not present in all caves; furthermore, anuran breeding biology is incredibly flexible in evolutionary terms, numerous lineages feeding or nourishing their tadpoles somehow, and many having abandoned the tadpole phase entirely. And, actually, there are several anurans that do frequent caves (examples: the North American Pickerel frog Lithobates palustris, Australian Cave-dwelling frog Litoria cavernicola and Puerto Rican Rock coqui or Guajón Eleutherodactylus cooki), it’s just that they frequent cave mouths and are not anywhere near as specialised as olms or other cave-dwelling salamanders. Cave caecilians? Hmm, not yet I think.

* Yes, there are anurans that have evolved acoustic signals that combat the problems of being close to waterfalls, and yes there are anurans that use visual signals (like waving their limbs around) in place of acoustic ones, but (1) these innovations are rare and restricted to a couple of unusual lineages, and (2) visual cues might not work well in pitch-darkness.

One last thing. Dan yr Ogof doesn’t just have models of cave-dwelling salamanders: there are two pale, cave-dwelling trout as well. I refuse to talk about them. Goddam fish.

About the Author: Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at darrennaish.wordpress.com. He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at tetzoo.com! Follow on Twitter @TetZoo.

33 Comments

It looks pretty evident that anurans can’t exhibit paedomorphosis (which is a shame), and I would agree that paedomorphosis makes it easier for salamanders to become cave specialists… but does this explain why anurans haven’t become cave specialists at all? I’m not sure. Of course, this speculation is invalid if there are stygobiontic anurans…

How about stygobiontic sauropsids, when we are on the subject? The more I think of it, the more it seems to me that salamanders might be unique or nearly so among tetrapods in this respect. While assessing degrees of neoteny among widely disparate taxa is very tricky, could we say that various salamanders are the most neotenic tetrapods and have indepedently from each other evolved to be that way to boot?

How about stygobiontic sauropsids, when we are on the subject? The more I think of it, the more it seems to me that salamanders might be unique or nearly so among tetrapods in this respect.

“Stygibiont” specifically indicates animals that dwell in underground water bodies. This isn’t exactly an ideal environment for squamates. Salamanders can get away with it because they have gills, but this is a hostile environment for most vertebrates.

It’s worth pointing out that there are really very few stygibiont salamanders out there. There’s Proteus in the Dinaric karsts, there’s a few lineages of Eurycea in karst systems in Texas, and there’s Gyrinophilus in karsts in the Appalachians. That’s basically it. You have a lot of salamanders that will live near the entrances (which are moist and dark and thus good salamander habitat), but very few are obligatory cave-dwellers. No salamandrids, no direct-developing plethodontids, no ambystomatids, no hynobiids, etc.

Karst in general is pretty hostile territory for vertebrates; there’s not always reliable oxygen, there’s extremely limited food, temperatures are stable but cold, and water will often have high concentrations of dissolved minerals that may have adverse effects on homeostasis. Moreover, most karst systems are relatively limited in geographic distribution, limiting your population size and possibly the permanence of your habitat.

@Christopher Taylor:
Wow, salamanders in Australia. When was the last time that happened? Do I correctly recall salamanders being present among the early Eocene Tingamarra fossils or is my memory playing tricks on me?

Thanks for the great comments – the tutorial on terminology is much appreciated, ectodysplasin. But isn’t it ‘stygobiont’, rather than ‘stygibiont’? I’ve seen both in the literature, but the former seems more widespread.

The Australian newt population: in answer to BrianL (comment # 9), I think this might be a first. I’ve said before that I think I recall someone mentioning an alleged fossil salamander (as in, a vertebra or something) from Riversleigh, but this has never panned out. So far as we know right now, it seems that Australia has always been caudate-free (Caudata: ‘caudates’ or ‘caudatans’? The former is most common).

@Darren:
Thanks, apparently my memory was not playing tricks on me, but the literature might have been.

In praise of newts, I would like to mention just how beautiful and magnificent Great Crested Newts are (my parents have a seemingly healthy population of them in their garden/ponds)and how fond I am of the underappreciated Iberian Ribbed Newt: Not a particularly graceful creature, but its size, massiveness, flamboyantly long and tall tail, those strange exposed rubs, the flat head and that voracious appetite certainly count for something. If you’ve never seen one search, find, attack and quickly devour a decently sized worm, I suggest you do so as soon as possible. It’s a sight to behold.

It’s all stygo- as far as I’m aware. Stygobiont refers to any member of the stygobiota, which includes stygophiles and stygoxenes as well.

The interesting thing about stygobites (compared with troglobites) is that stygobites often inhabit epikarst as well as open karst spaces. This mostly applies to amphipods and copepods, but might, might, might apply to Proteus where populations still seem to exhibit gene flow between cave systems.

Wow. Olm larvae traveling through epikarst? That would be awesome. Although I wonder if the genetic relationship between populations in different cave systems might be explained simply by people capturing and trading these animals as pets, and the release of unwanted ones in the nearest cave? After all, that’s how the French and German olm populations are supposed to have been established.

Speaking of introductions, aren’t there a few olms in an English cave? In Devon if memory serve…

Also I wonder if our own species can be considered troglophilic, considering the frequent use of caves, dugouts, rock shelters and troglodytic architecture by Homo sapiens, from paleolithic times onwards, on all five continents…

Gene flow between the stygobiont olms? (comment # 13). I thought that the exact opposite had been demonstrated: that the different populations were highly distinct and unique to specific watershed regions. This is from…

They don’t talk about gene flow between populations so far as I can see; in fact they state that “No haplotypes were shared among major groups, indicating the absence of recent gene flow among the groups” (p. 37). Would be interested to know if there are studies contradicting this.

As goes people moving olms around (comment # 14) – yes, lots of evidence for this. Regarding olms in Devon… really?? (I hope this is true: what’s your source?). I’ve mentioned before that I’ve seen British, Victorian-era books where they talk about obtaining olms for the aquarium, a statement which implies that olms were available for sale in the UK at the time. But I haven’t ever heard that any were released.

Mentions of salamanders in the early Eocene Tingamarra Local Fauna near Murgon, Queensland, mostly appear to derive from this page compiled by Anne Musser (monotreme anatomist) for the Australian Museum in connection with the Yowie Lost Kingdoms series. It would have been written in 2000 or so, with some later updates but not anything like current.
Earlier, in the January 1995 issue (No. 25) of Riversleigh Notes, Mike Archer’s ‘Riversleigh/Murgon Research Report for 1994′ has the following:
“Prof. Zgynik Rocek [sic] from the Academy of Science in Czechoslovakia shocked us to the core when he spotted salamander vertebrae among the postcranial bits from Murgon – and is now involved with us in a joint paper on this topic.”
However, nothing about the caudate fossil ever appeared in a journal and I seem to recall that Prof. (Zbynek) Roček changed his mind about it after a longer look, but even Riv Notes doesn’t have a mention of that fact. Don’t you hate it when that happens?

I’ve found the mention about possible UK olms in Wikipedia in the paragraph titled “Research history”:

“There are also several cave laboratories in Europe, where olms have been introduced and are being studied. These are Moulis, Ariège (France), Kent’s Cavern (England), Han-sur-Lesse (Belgium) and Aggtelek (Hungary).”

Wow, thanks much for this, irene I really must make a trip there, then. I’ve seen olms in their native habitat in Croatia, but I’d love to see them again. I’m in Devon very soon for social reasons, so will see if a visit to Kents Cavern [sic: they seem not to call it 'Kent's' any more] might be possible. Kents Cavern is well known for its Pleistocene fossils, by the way.

Gene flow between the stygobiont olms? (comment # 13). I thought that the exact opposite had been demonstrated: that the different populations were highly distinct and unique to specific watershed regions. This is from…

They don’t talk about gene flow between populations so far as I can see; in fact they state that “No haplotypes were shared among major groups, indicating the absence of recent gene flow among the groups” (p. 37). Would be interested to know if there are studies contradicting this.

Each of these watersheds represents a cave province, not necessarily a single cave system. So yes, there are ~6 genetically distinct populations of Proteus that are more or less watershed-restricted, but they aren’t cave system restricted. That paper was addressing the suggestion that all Proteus represents a single population, which is likely not the case.

We see something like this in the Texas karst Eurycea (E. robusta, E. rathbuni, etc) which all, more or less, represent independent colonizations of hypogean environments by surface-dwelling salamanders. It’s been suggested that this is what happened with Proteus, but Proteus lacks the diverse terrestrial and troglophilic/stygophilic forms of Eurycea.

Another possibility is that erosion and glaciation in he Dinarics chopped up more integrated cave systems. There are a number of caves up in the Canadian Rockies, for example, that were clearly chopped off of larger systems by the Pleistocene glaciation.

The third alternative is that Proteus really is doing something rather weird in the epikarst. It’s worth noting that Proteus are morphologically and physiologically pretty strange animals, and there’s little reason to believe that this weirdness can be explained by neoteny alone. It also differs from cave Eurycea in some key ways that would suggest Proteus is more fossorial than the Texan stygobites.

About possible fossorial behaviour in olms, it would be consistent with the fact that at least in one research station (Moulis, France), the animal was observed eating soil from the bottom of the water channels where they like. Juveniles especially seem to use the soil bacteria as a non-negligible source of food. Adults are more prone to rely on predation of small arthropods.

@22: If Olms are active at low temperatures, there’s another possibility. Glaciers have meltwater channels under them, and if Olms occupy disjunct caves in a watershed that used to be covered by a glacier, it’s possible that they crawled from cave to cave via channels beneath the glaciers during the last ice age.

Presumably someone knows just how cool Olms can get and still live, but if not, I suppose that someone can set up the equivalent of an Olm habitrail in a lab fridge somewhere and find out.

I recall reading that Olms kept in a normal aquarium and exposed to sunlight will actually grow darker, is this true? Does that mean they would come to look like Black Olms? If so, how certain can we be that Black Olms are truly a different clade from typical Olms instead of being a morphotype?

“Presumably someone knows just how cool Olms can get and still live, but if not, I suppose that someone can set up the equivalent of an Olm habitrail in a lab fridge somewhere and find out.”

According to Menager (2004), olms live ordinarily in conditions of cool but stable temperature, around 10 °C. Typically, deep enough for glacier meltwater to be be buffered by the rest of the aquifer. Olms have been observed in waters as cold as 5 °C but don’t breed at such low temperature.

@28: That’s good news. I suppose that if you want to find out how cold an olm (or other salamander) will tolerate, you could do something like the following experiment.

This assumes that you can maintain a stable gradient of water temperatures from 10oC down to 1oC across up to a meter of experimental spillway. The idea is to have water flowing, perhaps down a slight incline, from an area of extreme cold (close to freezing) down to an area at 10oC, where the olm is introduced. The water needs to be flowing, but slowly enough that the olm has no trouble walking or swimming against the current. Introduce a bait or similar scent attractant at the upstream, cold end of the spillway, and place the hungry salamander at the downstream, warm end of the spillway. If there’s no thermal gradient, the salamander should head upstream to the bait. With the cold gradient, the question is whether it will go all the way to the bait, or whether it will stop at some point. If the salamander stops before it gets to the bait, the temperature at which it stops is likely close to how cold it is willing to tolerate.

If an olm has no problem getting close to freezing and moving towards food, that suggests that it might migrate under a glacier if given the chance.

There was definitely no inland ice on the Balkan Peninsula. Indeed, it was a refuge from glaciation, together with the Iberian Peninsula; that’s why so many European mammals have an eastern and a western form.